U.S. patent number 11,430,631 [Application Number 16/833,463] was granted by the patent office on 2022-08-30 for methods of inspecting samples with multiple beams of charged particles.
This patent grant is currently assigned to ASML Netherlands B.V.. The grantee listed for this patent is ASML Netherlands B.V.. Invention is credited to Wei Fang, Jack Jau, Kuo-Shih Liu, Xuedong Liu.
United States Patent |
11,430,631 |
Liu , et al. |
August 30, 2022 |
Methods of inspecting samples with multiple beams of charged
particles
Abstract
Disclosed herein is a method comprising: generating a plurality
of probe spots on a sample by a plurality of beams of charged
particles; while scanning the plurality of probe spots across a
region on the sample, recording from the plurality of probe spots a
plurality of sets of signals respectively representing interactions
of the plurality of beams of charged particles and the sample;
generating a plurality of images of the region respectively from
the plurality of sets of signals; and generating a composite image
of the region from the plurality of images.
Inventors: |
Liu; Kuo-Shih (Fremont, CA),
Liu; Xuedong (San Jose, CA), Fang; Wei (Milpitas,
CA), Jau; Jack (Los Altos Hills, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
ASML Netherlands B.V. |
Veldhoven |
N/A |
NL |
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Assignee: |
ASML Netherlands B.V.
(Veldhoven, NL)
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Family
ID: |
1000006530451 |
Appl.
No.: |
16/833,463 |
Filed: |
March 27, 2020 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20200227233 A1 |
Jul 16, 2020 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/EP2018/075930 |
Sep 25, 2018 |
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62566177 |
Sep 29, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01J
37/265 (20130101); H01J 37/28 (20130101); H01J
2237/24495 (20130101) |
Current International
Class: |
H01J
37/28 (20060101); H01J 37/26 (20060101) |
Field of
Search: |
;250/306,307,311 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2011 187191 |
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Sep 2011 |
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JP |
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WO 2017/132435 |
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Aug 2017 |
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WO |
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Other References
International Search Report and Written Opinion issued in related
PCT International Application No. PCT/EP2018/075930, dated Mar. 19,
2019 (16 pgs.). cited by applicant.
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Primary Examiner: McCormack; Jason L
Attorney, Agent or Firm: Finnegan, Henderson, Farabow,
Garrett & Dunner, LLP
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims priority to International Application No.
PCT/EP2018/075930, filed Sep. 25, 2018, and published as WO
2019/063532 A1, which claims priority of U.S. application
62/566,177 which was filed on Sep. 29, 2017. The contents of these
applications are incorporated herein by reference in their
entireties.
Claims
What is claimed is:
1. A method comprising: generating a plurality of probe spots on a
sample by a plurality of beams of charged particles; while scanning
the plurality of probe spots across a region on the sample,
recording from the plurality of probe spots a plurality of sets of
signals respectively representing interactions of the plurality of
beams of charged particles and the sample; generating a plurality
of images of the region in its entirety, respectively from the
plurality of sets of signals, wherein an image comprises a
compilation of digital values representing magnitudes of signals at
corresponding locations of a probe spot; and generating a composite
image of the region in its entirety, from the plurality of
images.
2. The method of claim 1, wherein the plurality of probe spots have
different sizes or different intensities.
3. The method of claim 1, wherein the plurality of probe spots are
spaced apart.
4. The method of claim 1, wherein the plurality of probe spots have
movements relative to one another while being scanned.
5. The method of claim 1, wherein time periods during which the
plurality of probe spots are respectively scanned across the region
are different.
6. The method of claim 5, wherein the time periods are not
temporally continuous.
7. The method of claim 5, wherein the time periods have partial
overlaps.
8. The method of claim 5, wherein the plurality of sets of signals
are recorded not during an entirety of the time periods.
9. The method of claim 1, wherein each of the plurality of images
of the region is generated from only one of the plurality of sets
of signals.
10. The method of claim 1, wherein generating the plurality of
images of the region comprises digitizing the plurality of sets of
signals with respect to magnitudes of the signals or locations of
the plurality of probe spots.
11. The method of claim 1, wherein the plurality of images of the
region are compilations of digital values representing magnitudes
of the signals.
12. The method of claim 11, wherein the composite image of the
region is a compilation of averages of the digital values.
13. The method of claim 1, wherein generating the composite image
of the region comprises averaging the plurality of images of the
region.
14. The method of claim 13, wherein averaging the plurality of
images is by simple average, weighted average or running
average.
15. A computer program product comprising a non-transitory computer
readable medium having instructions recorded thereon, the
instructions when executed by a computer implementing the method of
claim 1.
Description
TECHNICAL FIELD
This disclosure relates to methods for inspecting (e.g., observing,
measuring, and imaging) samples such as wafers and masks used in a
device manufacturing process such as the manufacture of integrated
circuits (ICs).
BACKGROUND
A device manufacturing process may include applying a desired
pattern onto a substrate. A patterning device, which is
alternatively referred to as a mask or a reticle, may be used to
generate the desired pattern. This pattern can be transferred onto
a target portion (e.g., including part of, one, or several dies) on
the substrate (e.g., a silicon wafer). Transfer of the pattern is
typically via imaging onto a layer of radiation-sensitive material
(resist) provided on the substrate. A single substrate may contain
a network of adjacent target portions that are successively
patterned. A lithographic apparatus may be used for this transfer.
One type of lithographic apparatus is called a stepper, in which
each target portion is irradiated by exposing an entire pattern
onto the target portion at one time. Another type of lithography
apparatus is called a scanner, in which each target portion is
irradiated by scanning the pattern through a radiation beam in a
given direction while synchronously scanning the substrate parallel
or anti parallel to this direction. It is also possible to transfer
the pattern from the patterning device to the substrate by
imprinting the pattern onto the substrate.
In order to monitor one or more steps of the device manufacturing
process (e.g., exposure, resist-processing, etching, development,
baking, etc.), a sample, such as a substrate patterned by the
device manufacturing process or a patterning device used therein,
may be inspected, in which one or more parameters of the sample may
be measured. The one or more parameters may include, for example,
edge place errors (EPEs), which are distances between the edges of
the patterns on the substrate or the patterning device and the
corresponding edges of the intended design of the patterns.
Inspection may also find pattern defects (e.g., failed connection
or failed separation) and uninvited particles.
Inspection of substrates and patterning devices used in a device
manufacturing process can help to improve the yield. The
information obtained from the inspection can be used to identify
defects, or to adjust the device manufacturing process.
SUMMARY
Disclosed herein is a method comprising: generating a plurality of
probe spots on a sample by a plurality of beams of charged
particles; while scanning the plurality of probe spots across a
region on the sample, recording from the plurality of probe spots a
plurality of sets of signals respectively representing interactions
of the plurality of beams of charged particles and the sample;
generating a plurality of images of the region respectively from
the plurality of sets of signals; and generating a composite image
of the region from the plurality of images.
According to an embodiment, the plurality of probe spots have
different sizes or different intensities.
According to an embodiment, the plurality of probe spots are spaced
apart.
According to an embodiment, the plurality of probe spots have
movements relative to one another while being scanned.
According to an embodiment, time periods during which the plurality
of probe spots are respectively scanned across the region are
different.
According to an embodiment, the time periods are not temporally
continuous.
According to an embodiment, the time periods have partial
overlaps.
According to an embodiment, the plurality of sets of signals are
recorded not during an entirety of the time periods.
According to an embodiment, each of the plurality of images of the
region is generated from only one of the plurality of sets of
signals.
According to an embodiment, generating the plurality of images of
the region comprises digitizing the plurality of sets of signals
with respect to magnitudes of the signals or locations of the
plurality of probe spots.
According to an embodiment, the plurality of images of the region
are compilations of digital values representing magnitudes of the
signals.
According to an embodiment, the composite image of the region is a
compilation of averages of the digital values.
According to an embodiment, generating the composite image of the
region comprises averaging the plurality of images of the
region.
According to an embodiment, averaging the plurality of images is by
simple average, weighted average or running average.
According to an embodiment, the method further comprises generating
an additional spot on the sample from another beam of charged
particles.
According to an embodiment, the additional spot has a different
size or a different intensity from that of the plurality of the
probe spots.
According to an embodiment, the method further comprises charging
the region with electric charges, using the additional spot.
According to an embodiment, the method further comprises scanning
the additional spot before or while scanning the plurality of probe
spots.
According to an embodiment, no signal representing interactions of
the other beam and the sample is recorded from the additional
spot.
Disclosed herein is a computer program product comprising a
non-transitory computer readable medium having instructions
recorded thereon, the instructions when executed by a computer
implementing any of the above methods.
BRIEF DESCRIPTION OF FIGURES
FIG. 1 schematically shows an apparatus that can carry out charged
particle beam inspection.
FIG. 2A schematically shows an apparatus that can carry out charged
particle beam inspection using multiple beams of charge particles,
where the charged particles in the multiple beams are from a single
source (a "multi-beam" apparatus).
FIG. 2B schematically shows an alternative multi-beam
apparatus.
FIG. 2C schematically shows an alternative multi-beam
apparatus.
FIG. 3 schematically shows inspecting a sample using one beam of
charged particles.
FIG. 4 schematically shows inspecting a sample using multiple beams
of charged particles, according to an embodiment.
FIG. 5 schematically shows inspecting a sample using multiple beams
of charged particles, according to an embodiment.
FIG. 6 schematically shows image averaging, according to an
embodiment.
FIG. 7 schematically shows inspecting a sample using multiple beams
of charged particles, according to an embodiment.
FIG. 8 schematically shows inspecting a sample using multiple beams
of charged particles, according to an embodiment.
FIG. 9 shows a flowchart for a method of inspecting a sample using
multiple beams of charged particles, according to an
embodiment.
DETAILED DESCRIPTION
There are various techniques for inspecting the sample (e.g., a
substrate and a patterning device). One kind of inspection
techniques is optical inspection, where a light beam is directed to
the substrate or patterning device and a signal representing the
interaction (e.g., scattering, reflection, diffraction) of the
light beam and the sample is recorded. Another kind of inspection
techniques is charged particle beam inspection, where a beam of
charged particles (e.g., electrons) is directed to the sample and a
signal representing the interaction (e.g., secondary emission and
back-scattered emission) of the charged particles and the sample is
recorded.
As used herein, unless specifically stated otherwise, the term "or"
encompasses all possible combinations, except where infeasible. For
example, if it is stated that a database can include A or B, then,
unless specifically stated otherwise or infeasible, the database
can include A, or B, or A and B. As a second example, if it is
stated that a database can include A, B, or C, then, unless
specifically stated otherwise or infeasible, the database can
include A, or B, or C, or A and B, or A and C, or B and C, or A and
B and C.
FIG. 1 schematically shows an apparatus 100 that can carry out
charged particle beam inspection. The apparatus 100 may include
components configured to generate and control a beam of charged
particles, such as a source 10 that can produce charged particles
in free space, a beam extraction electrode 11, a condenser lens 12,
a beam blanking deflector 13, an aperture 14, a scanning deflector
15, and an objective lens 16. The apparatus 100 may include
components configured to detect the signal representing the
interaction of the beam of charged particles and a sample, such as
an E.times.B charged particle detour device 17, a signal detector
21. The apparatus 100 may also include components, such as a
processor, configured to process the signal or control the other
components.
In an example of an inspection process, a beam 18 of charged
particle is directed to a sample 9 (e.g., a wafer or a mask)
positioned on a stage 30. A signal 20 representing the interaction
of the beam 18 and the sample 9 is guided by the E.times.B charged
particle detour device 17 to the signal detector 21. The processor
may cause the stage 30 to move or cause the beam 18 to scan.
Charged particle beam inspection may have higher resolution than
optical inspection due to the shorter wavelengths of the charged
particles used in charged particle beam inspection than the light
used in optical inspection. As the dimensions of the patterns on
the substrate and the patterning device become smaller and smaller
as the device manufacturing process evolves, charged particle beam
inspection becomes more widely used. The throughput of charged
particle beam inspection is relatively low due to interactions
(e.g., the Coulomb effect) among the charged particles used
therein. More than one beam of charged particles may be used to
increase the throughput.
In an example, multiple beams of charged particles can
simultaneously scan multiple regions on a sample. The scanning of
the multiple beams may be synchronized or independent. The multiple
regions may have overlaps among them, may be tiled to cover a
continuous area, or may be isolated from one another. Signals
generated from the interactions of the beams and the sample may be
collected by multiple detectors. The number of detectors may be
less than, equal to, or greater than the number of the beams. The
multiple beams may be individually controlled or collectively
controlled.
Multiple beams of charged particles may form multiple probe spots
on a surface of a sample. The probe spots can respectively or
simultaneously scan multiple regions on the surface. The charged
particles of the beams may generate signals from the locations of
the probe spots. One example of the signals is secondary electrons.
Secondary electrons usually have energies less than 50 eV. Another
example of the signals is backscattered electrons when the charged
particles of the beams are electrons. Backscattered electrons
usually have energies close to landing energies of the electrons of
the beams. The signals from the locations of the probe spots may be
respectively or simultaneously collected by multiple detectors.
The multiple beams may be from multiple sources respectively, or
from a single source. If the beams are from multiple sources,
multiple columns may scan and focus the beams onto the surface, and
the signals generated by the beams may be detected by detectors in
the columns, respectively. An apparatus using beams from multiple
sources may be called as a multi-column apparatus. The columns can
be either independent or share a multi-axis magnetic or
electromagnetic-compound objective lens. See U.S. Pat. No.
8,294,095, whose disclosure is hereby incorporated by reference in
its entirety. The probe spots generated by a multi-column apparatus
may be spaced apart by a distance as large as 30-50 mm.
If the beams are from a single source, a source-conversion unit may
be used to form multiple virtual or real images of the single
source. Each of the images and the single source may be viewed as
an emitter of a beam (also called a "beamlet" as all of the
beamlets are from the same source). The source-conversion unit may
have an electrically conductive layer with multiple openings that
can divide the charged particles from the single source into
multiple beamlets. The source-conversion unit may have optics
elements that can influence the beamlets to form multiple virtual
or real images of the single source. Each of the images can be
viewed as a source that emits one of the beamlets. The beamlets may
be spaced apart by a distance of micrometers. A single column,
which may have a projection system and a deflection scanning unit,
may be used to scan and focus the beamlets on multiple regions of a
sample. The signals generated by the beamlets may be respectively
detected by multiple detection elements of a detector inside the
single column. An apparatus using beams from a single source may be
called as a multi-beam apparatus.
There are at least two methods to form the images of the single
source. In the first method, each optics element has an
electrostatic micro-lens that focuses one beamlet and thereby forms
one real image. See, e.g., U.S. Pat. No. 7,244,949, whose
disclosure is hereby incorporated by reference in its entirety. In
the second method, each optics element has an electrostatic
micro-deflector which deflects one beamlet thereby forms one
virtual image. See, e.g., U.S. Pat. No. 6,943,349 and U.S. patent
application Ser. No. 15/065,342, whose disclosures are hereby
incorporated by reference in their entirety. Interactions (e.g.,
the Coulomb effect) among the charged particles in the second
method may be weaker than that in the first method because a real
image has a higher current density.
FIG. 2A schematically shows an apparatus 400 that can carry out
charged particle beam inspection using multiple beams of charge
particles, where the charged particles in the multiple beams are
from a single source. Namely, the apparatus 400 is a multi-beam
apparatus. The apparatus 400 has a source 401 that can produce
charged particles in free space. In an example, the charged
particles are electrons and the source 401 is an electron gun. The
apparatus 400 has an optics system 419 that can generate with the
charged particles multiple probe spots on a surface of a sample 407
and scan the probe spots on the surface of the sample 407. The
optics system 419 may have a condenser lens 404 and a main aperture
405 upstream or downstream with respect to the condenser lens 404.
The expression "Component A is upstream with respect to Component
B" as used herein means that a beam of charged particles would
reach Component A before reaching Component B in normal operation
of the apparatus. The expression "Component B is downstream with
respect to Component A" as used herein means that a beam of charged
particles would reach Component B after reaching Component A in
normal operation of the apparatus. The optics system 419 has a
source-conversion unit 410 configured to form multiple virtual
images (e.g., virtual images 402 and 403) of the source 401. The
virtual images and the source 401 each can be viewed as an emitter
of a beamlet (e.g., beamlets 431, 432 and 433). The
source-conversion unit 410 may have an electrically conductive
layer 412 with multiple openings that can divide the charged
particles from the source 401 into multiple beamlets, and optics
elements 411 that can influence the beamlets to form the virtual
images of the source 401. The optics elements 411 may be
micro-deflectors configured to deflect the beamlets. The electric
current of the beamlets may be affected by the sizes of the
openings in the electrically conductive layer 412 or the focusing
power of the condenser lens 404. The optics system 419 includes an
objective lens 406 configured to focus the multiple beamlets and
thereby form multiple probe spots onto the surface of the sample
407. The source-conversion unit 410 may also have
micro-compensators configured to reduce or eliminate aberrations
(e.g., field curvature and astigmatism) of the probe spots.
FIG. 2B schematically shows an alternative multi-beam apparatus.
The condenser lens 404 collimates the charged particles from the
source 401. The optics elements 411 of the source-conversion unit
410 may comprise micro-compensators 413. The micro-compensators 413
may be separate from micro-deflectors or may be integrated with
micro-deflectors. If separated, the micro-compensators 413 may be
positioned upstream to the micro-deflectors. The micro-compensators
413 are configured to compensate for off-axis aberrations (e.g.,
field curvature, astigmatism and distortion) of the condenser lens
404 or an objective lens (such as the objective lens 406 of FIG.
2A). The off-axis aberrations may negatively impact the sizes or
positions of the probe spots formed by off-axis (i.e., being not
along the primary optical axis of the apparatus) beamlets. The
off-axis aberrations of the objective lens 406 may not be
completely eliminated by deflection of the beamlets. The
micro-compensators 413 may compensate for the residue off-axis
aberrations (i.e., the portion of the off-axis aberrations that
cannot be eliminated by deflection of the beamlets) of the
objective lens 406, or non-uniformity of the sizes of the probe
spots. Each of the micro-compensators 413 is aligned with one of
the openings in the electrically conductive layer 412. The
micro-compensators 413 may each have four or more poles. The
electric currents of the beamlets may be affected by the sizes of
the openings in the electrically conductive layer 412 and/or the
position of the condenser lens 404.
FIG. 2C schematically shows an alternative multi-beam apparatus.
The optics elements 411 of the source-conversion unit 410 may
comprise pre-bending micro-deflectors 414. The pre-bending
micro-deflectors 414 are micro-deflectors configured to bend the
beamlets before they go through the openings in the electrically
conductive layer 412.
Additional descriptions of apparatuses using multiple beams of
charge particles from a single source may be found in U.S. Patent
Application Publications 2016/0268096, 2016/0284505 and
2017/0025243, U.S. Pat. No. 9,607,805, U.S. patent application Ser.
Nos. 15/365,145, 15/213,781, 15/216,258 and 62/440,493, and PCT
Application PCT/US17/15223, the disclosures of which are hereby
incorporated by reference in their entirety.
When a region of a sample (e.g., a substrate or a patterning
device) is inspected with one beam of charged particles, a signal
representing the interactions of the beam and the sample is
recorded from the probe spot formed by the beam in the region. The
signal may include random noises. To reduce the random noises, the
probe spot may scan the region multiple times, and the signals
recorded from the same locations at different times may be
averaged. FIG. 3 schematically shows inspecting a sample using one
beam of charged particles. FIG. 3 shows the movement of the probe
spot 310 relative to the sample. The sample may move during
scanning of the probe spot 310. The diameter of the probe spot 310
is W. The region 300 to be inspected shown in this example is
rectangular in shape but not necessarily so. For convenience, two
directions x and y are defined in a reference frame ("RF") that has
no movement relative to the sample. The x and y directions are
mutually perpendicular. During time period T10, the probe spot 310
scans across the entirety of the region 300, which means that every
location in the region 300 is within the probe spot 310 at some
point of time during time period T10. For example, the probe spot
310 may move in the x direction by a length L (represented by solid
arrows), during which signals representing the interaction of the
beam and the sample are recorded from the probe spot 310; may move
in the -x direction by length L and in the -y direction by width W
(represented by dotted arrows), during which no signals
representing the interaction of the beam and the sample are
recorded from the probe spot 310. These back-and-forth movements of
the probe spot 310 may be repeated until the probe spot 310 scans
across the entirety of the region 300. Other movements of the probe
spot 310 to cover the entirety of the region may be possible. An
image 351 of the region 300 may be generated from the signals
recorded during time period T10. For example, the image 351 may be
generated by digitizing the signals in magnitude or in space. The
image 351 may be a compilation of digital values representing the
magnitudes of the signals recorded when the probe spot 310 was at a
plurality of locations within the region 300, respectively.
Although the word "image" is used, the image 351 is not necessarily
in a form readily perceivable by human eyes. For example, the image
351 may be values stored in a computer memory. Additional images
such as images 352 and 353 may be obtained during time periods such
as T20 and T30 that are different from time period T10, in the same
or different fashion. The time periods T10, T20 and T30 may not be
temporally continuous. The images obtained from the probe spot 310
generated by the same beam of charged particles are averaged (e.g.,
simple average, weighted average, running average, etc.). For
example, when the images 351, 352 and 353 are compilations of
digital values representing the magnitudes of the signals recorded
when the probe spot 310 was at a plurality of locations within the
region 300, averaging the images 351, 352 and 353 may be done by
averaging the digital values at the same location. Namely, the
average of the images 351, 352 and 353 may be a compilation of the
averages of the digital values of the images 351, 352 and 353
respectively at the plurality of locations.
FIG. 4 schematically shows inspecting a sample using multiple beams
of charged particles, according to an embodiment. In this example,
three beams generate three probe spots 310A-310C on a sample. FIG.
4 shows the movement of the three probe spots 310A-310C relative to
the sample. The three probe spots 310A-310C may be but not
necessarily arranged in a row. The width of the three probe spots
310A-310C is W in this example. The width of the probe spots is not
necessarily the same. The three probe spots 310A-310C may or may
not have movement relative to one another.
The region 300 to be inspected in this example is rectangular in
shape but not necessarily so. In this example, during time periods
T41, T42 and T43, the three probe spots 310A-310C are respectively
scanned across the entirety of the region 300, which means that
every location in the region 300 is within the probe spots
310A-310C at some point of time during time periods T41-T43,
respectively. For example, the three probe spots 310A-310C may move
in the x direction by a length L (represented by solid arrows),
during which signals representing the interaction of the beam and
the sample are recorded from the probe spots 310A-310C; move in the
-x direction by length L and in the -y direction by width W
(represented by dotted arrows), during which no signals
representing the interaction of the beam and the sample are
recorded from the three probe spots 310A-310C. These back-and-forth
movements may be repeated until each of the three probe spots
310A-310C is scanned across the entirety of the region 300. The
three probe spots 310A-310C may be at different locations at the
beginning of time period T41, T42 or T43 and the locations may be
outside the region 300. For example, as shown in FIG. 4, at the
beginning of time period T41, probe spot 310A is at the extreme of
the region 300 in the y direction; probe spot 310B is adjacent to
probe spot 310A and outside the region 300; probe spot 310C is
adjacent to probe spot 310B and further outside the region 300. The
three probe spots 310A-310C may be at different locations in the
duration of time period T41, T42 or T43. For example, as shown in
FIG. 4, at a time in the duration of time period T41, T42 or T43,
the probe spots 310A-310C are adjacent to one another and inside
the region 300. Similarly, the three probe spots 310A-310C may be
at different locations at the end of time period T43 and the
locations may be outside the region 300. For example, as shown in
FIG. 4, at the end of time period T43, probe spot 310C is at the
extreme of the region 300 in the -y direction; probe spot 310B is
adjacent to probe spot 310C and outside the region 300; probe spot
310A is adjacent to probe spot 310B and further outside the region
300. An image 361 of the region 300 may be formed from the signals
recorded from probe spot 310A during time period T41. An image 362
of the region 300 may be formed from the signals recorded from
probe spot 310B during time period T42. An image 363 of the region
300 may be formed from the signals recorded from probe spot 310C
during time period T43. For example, the images 361-363 may be
formed by digitizing the signals in magnitude or in space. The
images 361-363 may be a compilation of digital values representing
the magnitudes of the signals recorded when the probe spots
310A-310C were at a plurality of locations within the region 300,
respectively. Although the word "image" is used, the images 361-363
are not necessarily in a form readily perceivable by human eyes.
For example, the images 361-363 may be values stored in a computer
memory. The time periods T41, T42 and T43 may have some overlap (as
in this example), complete overlap (as in the example shown in FIG.
5), or no overlap at all. The time periods T41, T42 and T43 may not
be temporally continuous. In this example, the time periods T41,
T42 and T43 have the same length but begin at different time and
end at different time. The images 361-363 are averaged (e.g.,
simple average, weighted average, running average, etc.). For
example, when the images 361-363 are compilations of digital values
representing the magnitudes of the signals recorded when the probe
spots 310A-310C were at a plurality of locations within the region
300, averaging the images 361-363 may be done by averaging the
digital values at the same location. Namely, the average of the
images 361-363 may be a compilation of the averages of the digital
values of the images 361-363 respectively at the plurality of
locations. In this example, no two of the three probe spots
310A-310C are at the same location in the region 300 at the same
time when signals representing the interaction of the beams that
generated these two probe spots and the sample are recorded.
FIG. 5 schematically shows inspecting a sample using multiple beams
of charged particles, according to an embodiment. In this example
shown, three beams generate three probe spots 310A-310C on a
sample. FIG. 5 shows the movement of the three probe spots
310A-310C relative to the sample. The three probe spots 310A-310C
may be but not necessarily arranged in a row. The width of the
three probe spots 310A-310C is W in this example. The width of the
probe spots is not necessarily the same. The three probe spots
310A-310C may or may not have movement relative to one another. The
region 300 to be inspected shown in this example is rectangular in
shape but not necessarily so. In this example, during time period
T40, each of the three probe spots 310A-310C is scanned across the
entirety of the region 300, which means that every location in the
region 300 is within each of the probe spots 310A-310C at some
point of time during time period T40. For example, the three probe
spots 310A-310C may move in the x direction by a length L
(represented by solid arrows), during which signals representing
the interaction of the beam and the sample are recorded from the
probe spots 310A-310C; move in the -x direction by length L and in
the -y direction or the y direction by one or multiples of width W
(represented by dotted arrows), during which no signals
representing the interaction of the beam and the sample are
recorded from the three probe spots 310A-310C. These back-and-forth
movements may be repeated until each of the three probe spots
310A-310C scans across the entirety of the region 300. The three
probe spots 310A-310C may be at different locations at the
beginning of time period T40. For example, as shown in FIG. 5, at
the beginning of time period T40, probe spot 310C is at the extreme
of the region 300 in the y direction; probe spot 310B is adjacent
to probe spot 310C and inside the region 300; probe spot 310A is
adjacent to probe spot 310B and further inside the region 300.
Similarly, the three probe spots 310A-310C may be at different
locations during or at the end of time period T40. An image 361 of
the region 300 may be formed from the signals recorded from probe
spot 310A during time period T40. An image 362 of the region 300
may be formed from the signals recorded from probe spot 310B during
time period T40. An image 363 of the region 300 may be formed from
the signals recorded from probe spot 310C during time period T40.
For example, the images 361-363 may be formed by digitizing the
signals both in magnitude and in space. The images 361-363 may be a
compilation of digital values representing the magnitudes of the
signals recorded when the probe spots 310A-310C were at a plurality
of locations within the region 300, respectively. Although the word
"image" is used, the images 361-363 are not necessarily in a form
readily perceivable by human eyes. For example, the images 361-363
may be values stored in a computer memory. The time period T40 may
not be temporally continuous. The images 361-363 are averaged
(e.g., simple average, weighted average, running average, etc.).
For example, when the images 361-363 are compilations of digital
values representing the magnitudes of the signals recorded when the
probe spots 310A-310C were at a plurality of locations within the
region 300, averaging the images 361-363 may be done by averaging
the digital values at the same location. Namely, the average of the
images 361-363 may be a compilation of the averages of the digital
values of the images 361-363 respectively at the plurality of
locations. In this example, no two of the three probe spots
310A-310C are at the same location in the region 300 at the same
time when signals representing the interaction of the beams that
generated these two probe spots and the sample are recorded.
FIG. 6 schematically shows image averaging, according to an
embodiment. Multiple sets (e.g., sets 611-613) of signals are
recorded from multiple probe spots (e.g., probe spots 310A-310C)
during multiple time periods (e.g., time periods T41-T43). The sets
of signals may be analog signals in the example shown here. Images
(e.g., images 661-663) may be formed by respectively digitizing the
sets of signals both in magnitude and in space. The values and
shades shown in this example represent the magnitudes of digitized
signals. An averaged image (e.g., averaged image 669) is formed by
averaging the magnitudes of digitized signals at the corresponding
locations in the images Other methods of averaging are
possible.
FIG. 7 schematically shows inspecting a sample using multiple beams
of charged particles, according to an embodiment. In this example
shown here, which is similar to the example in shown in FIG. 5,
three beams generate three probe spots 310A-310C on a sample. FIG.
7 shows the movement of the three probe spots 310A-310C relative to
the sample. In the example shown in FIG. 5, the probe spots
310A-310C are adjacent to one another. In the example shown in FIG.
7, the three probe spots 310A-310C may be spaced apart, for
example, by multiples of width W. Having the probe spots 310A-310C
spaced apart may reduce interactions of the beams that generate the
probe spots 310A-310C, or interference of the signals recorded from
the probe spots 310A-310C.
FIG. 8 schematically shows inspecting a sample using multiple beams
of charged particles, according to an embodiment, where one or more
additional beams of charged particles may be used for other
purposes than generating signals for imaging. The example shown in
FIG. 8 is similar to the example shown in FIG. 4 but has a spot
310D generated on the sample by an additional beam of charged
particles for charging the region 300 with electric charges before
the probe spots 310A-310C scan across the region 300. The spot 310D
may have a different size or a different intensity than the probe
spots 310A-310C. The spot 310D may scan the region 300 before or
while the probe spots 310A-310C scan the region 300. In an
embodiment, no signal is recorded from the spot 310D.
FIG. 9 shows a flowchart for a method of inspecting a sample using
multiple beams of charged particles, according to an embodiment. In
procedure 910, a plurality of probe spots 920 are generated on the
sample by a plurality of beams of charged particles. The plurality
of probe spots 920 may have the same size or different sizes. The
plurality of probe spots 920 may have the same intensity or
different intensities. The plurality of probe spots 920 may be
adjacent to one another or spaced apart. Additional spots may be
generated on the sample by additional beams of charged particles,
and may have different sizes or intensities from that of the probe
spots 920. In procedure 930, while the probe spots 920 are scanned
across a region on the sample, a plurality of sets of signals 940
respectively representing the interactions of the plurality of
beams of charged particles and the sample are recorded from the
probe spots 920. The probe spots 920 may have movements relative to
one another while the probe spots 920 are scanned across the
region. The probe spots 920 may be scanned across the region during
different time periods. The probe spots 920 may be scanned across
different parts of the region without scanning the region in
between. The sets of signals 940 may be recorded not all the time
while the probe spots 920 are scanned across the region. In
procedure 950, a plurality of images 960 of the region are
generated respectively from the sets of signals 940. Each of the
images 960 may be generated from only one of the sets of signals
940. The images 960 may be generated by digitizing the sets of
signals 940 with respect to the magnitudes of the signals and the
locations of the probe spot 920. The images 960 may have pixels of
finite sizes. The images 960 may not be in a form readily
perceivable by human eyes. For example, the images 960 may be
compilations of digital values representing magnitudes of the
signals, stored in computer readable storage media. In procedure
970, a composite image 980 of the region is generated from the
plurality of images 960. The composite image 980, like the images
960, may not be in a form readily perceivable by human eyes. In an
example, the composite image 980 may be a compilation of averages
of the digital values of the images 960.
The embodiments may further be described using the following
clauses:
1. A method comprising:
generating a plurality of probe spots on a sample by a plurality of
beams of charged particles;
while scanning the plurality of probe spots across a region on the
sample, recording from the plurality of probe spots a plurality of
sets of signals respectively representing interactions of the
plurality of beams of charged particles and the sample;
generating a plurality of images of the region respectively from
the plurality of sets of signals; and
generating a composite image of the region from the plurality of
images.
2. The method of clause 1, wherein the plurality of probe spots
have different sizes or different intensities.
3. The method of clause 1, wherein the plurality of probe spots are
spaced apart.
4. The method of clause 1, wherein the plurality of probe spots
have movements relative to one another while being scanned.
5. The method of clause 1, wherein time periods during which the
plurality of probe spots are respectively scanned across the region
are different.
6. The method of clause 5, wherein the time periods are not
temporally continuous.
7. The method of clause 5, wherein the time periods have partial
overlaps.
8. The method of clause 5, wherein the plurality of sets of signals
are recorded not during an entirety of the time periods.
9. The method of clause 1, wherein each of the plurality of images
of the region is generated from only one of the plurality of sets
of signals.
10. The method of clause 1, wherein generating the plurality of
images of the region comprises digitizing the plurality of sets of
signals with respect to magnitudes of the signals or locations of
the plurality of probe spots.
11. The method of clause 1, wherein the plurality of images of the
region are compilations of digital values representing magnitudes
of the signals.
12. The method of clause 11, wherein the composite image of the
region is a compilation of averages of the digital values.
13. The method of clause 1, wherein generating the composite image
of the region comprises averaging the plurality of images of the
region.
14. The method of clause 13, wherein averaging the plurality of
images is by simple average, weighted average or running
average.
15. The method of clause 1, further comprising generating an
additional spot on the sample from another beam of charged
particles.
16. The method of clause 15, wherein the additional spot has a
different size or a different intensity from that of the plurality
of the probe spots.
17. The method of clause 15, further comprising charging the region
with electric charges, using the additional spot.
18. The method of clause 15, further comprising scanning the
additional spot before or while scanning the plurality of probe
spots.
19. The method of clause 15, wherein no signal representing
interactions of the other beam and the sample is recorded from the
additional spot.
20. A computer program product comprising a non-transitory computer
readable medium having instructions recorded thereon, the
instructions when executed by a computer implementing the method of
any of clauses 1-19.
Although the disclosure above is made with respect to multi-beam
apparatuses (i.e., apparatuses that can carry out charged particle
beam inspection using multiple beams of charge particles, where the
charged particles in the multiple beams are from a single source),
the embodiments may be applicable in multi-column apparatuses
(i.e., apparatuses that can carry out charged particle beam
inspection using multiple beams of charge particles, where the
multiple beams of charge particles are produced from multiple
sources). Additional descriptions of multi-column apparatuses may
be found in U.S. Pat. No. 8,294,095, the disclosure of which is
hereby incorporated by reference in its entirety.
While the concepts disclosed herein may be used for inspection on a
sample such as a silicon wafer or a patterning device such as
chrome on glass, it shall be understood that the disclosed concepts
may be used with any type of samples, e.g., inspection of samples
other than silicon wafers.
The descriptions above are intended to be illustrative, not
limiting. Thus, it will be apparent to one skilled in the art that
modifications may be made as described without departing from the
scope of the claims set out below.
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